Generally, the present invention relates to an engine. More particularly, the present invention relates to an engine that has a variable compression ratio.
The compression ratio of an engine plays an important role in determining the output torque of the engine. The compression ratio is defined as a ratio of a combustion chamber volume C1 when a piston is at top dead center (TDC) to a combustion chamber volume C1+L1 when the piston is at bottom dead center (BDC). Here, L1 denotes a displacement of a cylinder.
Such a compression ratio can be formalized as the following equation 1.                                           C            1                    +                      L            1                                    C          1                                    (                  Equation          ⁢                      xe2x80x83                    ⁢          1                )            
According to the prior art, when a layout of an engine is designed, such a compression ratio is decided, and accordingly the engine is operated with the compression ratio in all its operating conditions. That is, according to the prior art, a compression ratio of an engine is fixed regardless of the engine operation conditions.
If a compression ratio of an engine can be varied in accordance with operational conditions of the engine, the performance thereof can be optimized with respect to various operating conditions.
For example, under a condition of a high compression ratio, it is preferable that ignition timing is advanced for maximizing output torque of the engine. However, the advance of ignition timing is limited by a possibility of knocking. Under a condition of a low speed and a low (or partial) load, it is preferable that the compression ratio is lowered for enhancing brake specific fuel consumption (BSFC) of the engine.
Therefore, if the compression ratio of an engine can be varied in accordance with operation conditions, enhancement of output power and fuel consumption in accordance with the operation conditions may be realized.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known in this country to a person of ordinary skill in the art.
Embodiments of the present invention provide an engine having non-limiting advantages of a variable compression ratio.
An exemplary engine having a variable compression ratio according to an embodiment of the present invention includes a guider formed above a main bearing supporting a crankshaft, a cylinder block having a connection portion for movably supporting the guider, an actuator disposed to the main bearing, for moving the main bearing in accordance with an operation condition of the engine such that the crankshaft is in-line with or offset from a reciprocating center of the piston, and an electronic control unit for operating the actuator.
In a further embodiment, the connection portion includes a guide groove within which the guider is movably engaged with.
In another embodiment, the actuator moves the main bearing to be offset from the reciprocating center of the piston when the operation conditions are low speed and low load, and the actuator moves the main bearing to be in-line with the reciprocating center of the piston when the operation conditions are high speed and high load.